1. Field of the Invention
The present invention relates to an apparatus and method for detecting a rotation angular speed and to an automobile using the apparatus. In particular, the present invention relates to an apparatus and method for detecting a rotation angular speed to reduce a measurement error when a rotation angular speed is low, and to an automobile using a rotation angular speed of a steering wheel detected by the apparatus to stabilize a vehicle.
2. Description of the Prior Art
In recent years, an automobile has been performing total vehicle stability control such as braking control, suspension control and traction control for stabilizing a vehicle so that the driver can drive the automobile safely and comfortably. The total vehicle stability control detects the rotation angle of a steering wheel by a rotation angle sensor, detects a rotation angular speed (a rotating speed) of the steering wheel by a rotation angular speed detection apparatus from a traveling amount of the detected rotation angle per predetermined time, and predicts the traveling direction intended by the driver (the direction to finish turning the steering wheel) by the detected rotation angular speed so as to perform the vehicle stability control based on the prediction.
A prior art rotation angular speed detection apparatus has a receiving part for receiving an angular signal from a rotation angle sensor outputting an angular signal corresponding to the rotation angle of a rotating body, for example, at intervals of 400 microseconds, a storage part for storing a first angle based on the received angular signal, a sending part for sending the first angle at intervals of 10 milliseconds, and a control part for determining a difference between the first angle stored immediately before sending the same and a second angle stored immediately before sending the first angle which is then multiplied by 100 (1 second/10 milliseconds) so as to detect a rotation angular speed (degrees/sec)
When the rotation angular speed detection apparatus is used in an automobile, an angular signal from an angle sensor outputting an angular signal corresponding to the rotation angle of a steering wheel is detected described above. Then, a rotation angular speed signal based on the detected rotation angular speed is calculated, for example, at intervals of 10 milliseconds to send the result to vehicle stability control to stabilize the vehicle.
Between the rotation angle actually rotating the rotating body and the rotation angle stored in the storage part, there are caused a measurement error of the rotation angle due to the accuracy of the rotation angle sensor, an error at reception due to electric delay, and an error at conversion of an analog signal to a digital signal. It is difficult to remove these errors. For example, when the total of these errors is a maximum of 0. 2xc2x0, a rotation angular speed is calculated by the abovementioned calculation, an error of 20 (degrees/sec) may be caused. This error has an error rate of 2% when the rotating body is rotated largely and for example, a difference of the rotation angles at intervals of 10 ms is 10xc2x0 (1000 degrees/sec), which is not very important. This error has an error rate of 20% when the rotation amount of the rotating body is relatively small and for example, a difference of the rotation angles at intervals of 10 ms is 1xc2x0 (100 degrees/sec). In this manner, when the rotation angular speed for actually rotating the rotating body is low, the error rate. of the detected rotation angular speed is very high.
When the rotation angular speed detection apparatus is used in an automobile, the rotation angular speed of the steering wheel detected by the rotation angular speed detection apparatus is sent to the vehicle stability control system of the. automobile. For example,, when the steering wheel is turned at a small angle when driving the automobile at high speed on an expressway, the error of the rotation angular speed sent to the vehicle stability control system is increased. The vehicle stability control misjudges that the steering wheel is turned abruptly and performs unnecessary traction control, so that the vehicle is unstable.
The present invention solves the problem above and accordingly, an object of the present invention is to provide an apparatus and method capable of detecting a rotation angular speed to reduce an error when the rotation angular speed for rotating a rotating body is low, and an automobile which can be driven more safely when a steering wheel is turned slowly.
To solve the foregoing problems, in the present invention, a rotation angular speed detection apparatus comprises: a receiving part for receiving an angular signal at predetermined time intervals from a rotation angle sensor for detecting a rotation angle of a rotating body with respect to the reference angle; a storage part for storing the rotation angle based on the received angular signal; and a control part for dividing a difference between a first arbitrary angle of the rotation angles stored in the storage part and a second angle stored before the first angle by the time required from storing of the second angle to storing of the first angle so as to detect a rotation angular speed; wherein when the difference between the first angle and the second angle is less than a predetermined value, the control part determines, from the angles stored in the storage part, a third angle stored before the second angle in which a difference between the first angle and the third angle is more than the predetermined value, and wherein the control part divides the difference between the first angle and the third angle by the time required from storing of the third angle to storing of the first angle so as to detect a rotation angular speed.
Such a construction can divide the difference between the rotation angles so as to reduce an error and detect a rotation angular speed having high accuracy.
In the present invention, when an angle in which a difference between the first angle and the angle is more than the predetermined value is not present in the rotation angles stored in the storage part, the control part selects an arbitrary rotation angle of the rotation angles stored in the storage part as a fourth angle, and divides a difference between the first angle and the fourth angle by the time required from storing of the fourth angle to storing of the first angle so as to detect a rotation angular speed.
Such a construction can detect a rotation angular speed having high accuracy when the rotating body is hardly rotated. In addition, the control part selects the rotation angle stored at the first of the rotation angles stored in the storage part as the fourth angle, and divides a difference between the first angle and the fourth angle by the time required from storing of the fourth angle to storing of the first angle so as to detect a rotation angular speed. A rotation angular speed having higher accuracy can be detected.
In the present invention, when a sign of the difference between the first angle and the second angle is reversed from a sign of the difference between the second angle and the rotation angle stored immediately before the second angle, the control part erases the rotation angles before the second angle of the rotation angles stored in the storage part.
Such a construction can detecta rotation angular speed having high accuracy when the forward/rearward rotation of the rotating body is repeated frequently in a short time.
An automobile of the present invention comprises: the rotation angular speed detection apparatus; and a vehicle stability control system for stabilizing a vehicle; wherein the rotation angular speed detection apparatus receives an angular signal from an angle sensor detecting a rotation angle of a steering wheel so as to detect a rotation angular speed of the steering wheel, and wherein a rotation angular speed signal based on the detected rotation angular speed is sent to the vehicle stability control system.
Such a construction can provide an automobile which can predict the traveling direction intended by the driver more precisely and permits suitable vehicle stability control.